which looks at the quantity and varieties of invertebrates, angiosperms and fish. Chemical status, which compares the concentrations of various chemicals against known safe concentrations, is rated good or fail. Parts of the Crouch are designated as "heavily modified", which means that the channels have been altered by human activity, and the criteria for this designation are defined by the Water Framework Directive. The water quality of the River Crouch was as follows in 2019. Reasons for the water quality being less than good include runoff from agricultural land, runoff from the transport infrastructure, and discharge from sewage treatment works. Like many rivers in the UK, the chemical status changed from good to fail in 2019, due to the presence of polybrominated diphenyl ethers (PBDE) and mercury compounds, neither of which had previously been included in the assessment. Gallery See also Bridgemarsh Island Wallasea Island Foulness Island References Bibliography External links Crouch Harbour Authority Crouch, River Borough of Basildon City of Chelmsford Ramsar sites in England